Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or a laser printer, and more particularly, to a method of conveying a jammed sheet when a sheet jam occurs in the vicinity of a fixing device.
Description of the Related Art
A phenomenon or a state in which a recording material is not smoothly conveyed to cause clogging, or is retained in a conveyance path in an image forming apparatus is referred to as a jam. For example, after a recording material passes through a fixing nip portion between a fixing roller and a pressure roller of a fixing device, if a leading edge of the recording material stops for some reason and the fixing roller continues to rotate, the recording material is jammed to the leading edge side into the shape of accordion pleats, and is retained. Further, if the fixing roller still continues to rotate, there may be cases in which the recording material bends midway to be wound around the fixing roller (this state is hereinafter referred to as winding jam). If a recording material is wound around the fixing roller, it is difficult to remove the wound recording material. Therefore, when a jam is detected, control is hitherto performed so that the conveyance of the recording material may be stopped as promptly as possible.
For example, in Japanese Patent Application Laid-Open No. 2004-253177, there is disclosed an externally heating type fixing device of an image forming apparatus, which is configured to bring a heating member into contact with a surface of a fixing roller to externally heat the fixing roller, and heat an unfixed toner image on a recording material by the heated fixing roller. In such an externally heating type fixing device, if the conveyance of the recording material is immediately stopped when a winding jam occurs, the bent recording material is not wound around the fixing roller, and is conveyed separately from the fixing roller in a state of being bent midway. Further, for example, in Japanese Patent Application Laid-Open No. 2011-64802, there is disclosed a technology in which, in order to solve a jam by removing a jammed sheet with ease, when a jam occurs, the conveyance is immediately stopped except for a load in the vicinity of an entrance of a post-processing device into which the recording material is introduced, and the conveyance of the load in the vicinity of the entrance of the post-processing device is stopped after a predetermined time period elapses.
In the externally heating type fixing device described above, if the conveyance is immediately stopped except for the load in the vicinity of the entrance of the device when a winding jam occurs, a user who opens a cover of the image forming apparatus in order to remove the jammed sheet visually recognizes the jammed sheet in the following state. Specifically, the user visually recognizes both a bent tip of the recording material that is conveyed separately from the fixing roller, and a trailing edge of the recording material. It is likely that, when the user opens the cover, the user grabs an end portion of the recording material that is visually recognized sooner to remove the recording material. When the grabbed end portion is the trailing edge of the recording material, if the user pulls the end portion in order to remove the recording material, the fixing roller rotates in a direction opposite to a normal direction of recording material conveyance. At that time, the recording material may be torn and the torn piece of the recording material may remain in the image forming apparatus to adversely affect the image forming apparatus. Therefore, in an image forming apparatus having an externally heating type fixing device, it has been desired to allow a user to remove a jammed sheet with ease when a winding jam occurs.